The present invention relates to carburetors for small internal combustion engines and more particularly, to fuel primers for providing fuel to the metering chamber of the carburetor prior to the starting of the internal combustion engine.
Small internal combustion engines, especially those on chain saws, lawn mowers, trimmers, leaf blowers and the like, generally need to be primed before starting of the engine occurs. Priming is the predrawing of fuel into the metering chamber of the carburetor prior to the starting of the internal combustion engine. Generally, after an internal combustion engine has sat for a long period of time, e.g. two weeks or greater, fuel in the metering chamber evaporates. This evaporation of fuel necessitates priming of the metering chamber so that fuel is present to start the engine. A dry metering chamber generally causes the operator to pull on the starting cord several more times than he would if the metering chamber contains a supply of fuel.
Several types of carburetor fuel primers have been suggested in the past and have accomplished the priming of the metering chamber. Typically, these types of primers are of an open loop design. The open loop enables fuel, after the metering chamber is primed, to enter into the atmosphere or to check back into the fuel tank. These open loop designs are entirely dependent upon the check valve sealability at the outlet side of the primer. This is of much concern, since in such devices the metering chamber has direct continuity to the outside atmosphere, which is abnormal to typical diaphragm type carburetor designs. If air is allowed to enter the metering chamber at the outlet point of the primer due to check valve leakage, this will have adverse effect on the normal function of the carburetor. The disadvantages of these types of primers are that the idle fuel mixture becomes lean and results in poor engine acceleration and/or idle stability. Also, in some instances, the air leak will cause the engine to stop running while in the idle mode.
Other types of conventional primer designs provide for a third one way check valve at the metering chamber fuel exit point. This valve feeds the idle system and nozzle high speed system with fuel. This design utilizes high speed nozzle valve, which normally functions in a one way direction, for passage of fuel and adding of the third check valve is considered redundant.
Accordingly, it is an object of the present invention to overcome the disadvantages of the above art. The present invention provides the art with a closed loop carburetor fuel primer. The present invention, due to the sealed closed loop, does not effect the normal functioning of the carburetor. The present invention enables the operator to prime the system without releasing any fuel to atmosphere. Also, the present invention enables fuel to be drawn into the metering chamber through the carburetor fuel inlet system, which is the normal route of the fuel, and the carburetor is not vented to atmosphere which places the carburetor in its normally functioning mode at all times.
The carburetor fuel primer of the present invention is associated with a metering chamber of a carburetor. The metering chamber generally has an inlet and an outlet associated with it. The metering chamber is coupled to a fuel source by the carburetor fuel inlet system, which is the normal fuel path into the carburetor. Also, the metering chamber is associated with the carburator venturi through primary fuel discharge ports and idling fuel discharge ports. The fuel primer includes a mechanism for enabling restricted one way flow into the metering chamber coupled with the metering chamber inlet. A second mechanism for enabling one way relatively unrestricted flow from the metering chamber is coupled with the metering chamber outlet. A third mechanism for producing pressurized and depressurized flow through the fuel primer is coupled with the first and second mechanisms.
In another embodiment of the present invention the fuel primer includes a plate member secured to the carburetor, by conventional means, covering the metering chamber. A restricted inlet and a relatively unrestricted outlet (or compared with the size of the inlet) are associated with the face of the plate member adjacent to the interior of the metering chamber. A passageway is present in the plate member for coupling the inlet and outlet. A mechanism coupled with the passageway pressurizes and depressurizes flow through the passage way. One way check valves are positioned in the passageway for metering flow into and out of the metering chamber through the restricted inlet and unrestricted outlet, respectively. When the system is pressurized, flow enters the metering chamber through the restricted inlet. With the metering chamber absent of fuel, air will be allowed to flow into metering chamber via the restricted inlet. With the restriction at the inlet, there is very little pressure buildup in the metering chamber, which prevents flow from exiting the nozzle and idle outlet passages.
Upon depressurizing, the flow exits the metering chamber through the primer unrestricted outlet. Since this outlet is unrestricted, a substantial vacuum exists during the depressurizing cycle of the primer system. Therefore, fuel is pulled from the normal fuel inlet passage.
As the primer cycle is repeated several times, most of the air will exit the nozzle and idle ports, while being replaced with fuel. Air (being of considerably less density) will pass the nozzle and idle port during the pressurizing mode of primer, while fuel (being of greater density) will not exit the nozzle and idle ports and will instead flow out the unrestricted outlet. This is accomplished by controlling the amount of pressure buildup in the metering chamber during the pressurization mode at the primer bulb. The pressure control is accomplished by greatly restricting the metering chamber primer inlet.
From the following description and claims taken in conjunction with the accompanying drawings, other objects and advantages of the present invention will become apparent to one skilled in the art.